Although this method provides a high resolution with a coherent-state input, the performance of imaging is still shot-noise-limited due to the shot noise of the coherent state (in fact, the performance of imaging is related to the quantum noise of the focused beam illuminating the object. When the coherent states are considered as input, the focused beam is still a coherent state [1]}). To circumvent this problem, one possible way is to reduce the shot noise. Fortunately, the shot noise is actually a classical limit which can be beaten by the quantum technique [2]}, [3]}, [4]}.
